An Air Canada spokesman said the wheel is believed to have fallen off the bearing on the runway in Montreal.

“None of the passengers knew what had happened and neither did the pilot, he was in shock when he landed and was told about the wheel.”

The plane is now grounded at Heathrow while it is inspected and repaired.

A spokesman for Air Canada told “Preliminary information indicates that a wheel separated from the aircraft while taxiing down the runway before take-off in Montreal and came to rest beside the runway.

“As the landing gear is comprised of 8 wheels, this had no impact on the safe operation of the flight.

“Flight AC864 an A330 with 294 passengers on board landed normally in London and taxied to the gate.

“Passengers on the returning flight are being re-booked on other flights later today while the aircraft is being repaired.”